fetch-field

Arguments: message part info &key uid

This function is used to extract the desired information from the
value returned by fetch-letter. With fetch-letter, you can
retrieve a variety of information about one or more messages and
fetch-field can
search through that information and return a particular piece of
information about a particular letter.

message is the message number (it's
assumed to be a message sequence number unless
uid is true, in which case it's a unique
id).

part is the type of information
desired. It is a string just as used in the call to fetch-letter.